There has long been a need to employ catalysts in the process of fuel combustion leading to simultaneous oxidation of carbon monoxide (CO) and unburned hydrocarbons, and the reduction of nitrogen oxides (NOx) (three-way catalysis) which are emitted from automotive engines and the like. The role of catalysts, particularly three-way catalysts, in automotive emission control has been widely studied in the art. For example, Taylor, "Automobile Catalytic Converter", Catalysis, Science and Technology, pp 119-67 (Anderson et al. eds. 1984), describes emissions control technology, composition of three-way catalysts, and catalytic supports.
Conventional systems for converting automotive exhaust gases employ pre-fabricated supported catalysts, typically a solid stratum of catalytic material, supported on ceramic or metallic substrates, which are placed in the exhaust section of the automobile. In prior art catalytic converter vessels, the substrate, ceramic or metallic, is pre-fabricated with a washcoat layer of catalyst, which layer then is the site for catalytic conversion. As the emissions pass through the solid, the catalytic metal present on the strata aids in conversion of CO, NOx and unburned hydrocarbons to CO.sub.2, N.sub.2 and H.sub.2 O. However, the solid strata-type catalytic converter eventually becomes spent, and requires removal and replacement in the exhaust portion of the engine. State of the art systems capable of carrying out three-way catalysis include those having supported rhodium and platinum, with noble metals such as rhodium being a preferred catalyst for the reaction: EQU NO+CO.fwdarw.1/2 N.sub.2 +CO.sub.2
Platinum is the preferred catalyst for the oxidation of CO and unburned hydrocarbons.
The noble metals are expensive and in limited supply, particularly rhodium. This is exacerbated by the fact that current usage of rhodium in three-way catalysis exceeds the Rh/Pt mine ratio. Thus, reduction of noble metal usage is a problem of three-way catalysis. Therefore, it is necessary to develop alternative approaches to emission control.
Accordingly, there is a need for alternative catalytic vessels capable of converting automotive emissions not utilizing conventional additional, pre-fabricated, washcoated catalytic converters in the exhaust system of an automobile. There is likewise a need for alternative catalytic vessels containing metal catalysts which convert emissions with increased efficiency in order to decrease the required supply of catalyst.